The present embodiments pertain to a novel imaging member, namely, an imaging member or photoreceptor comprising a protective outer layer which comprises light-blocking composition that substantially prevents any light absorption by the overcoat layer. The composition comprises a low strength thermal plastic resin and a high optical density yellow dye with a molar extinction coefficient of 5000 M−1 cm−1 or higher. In this manner, the light-blocking protective layer reduces the intrinsic light shock suffered by conventional overcoat layers without negatively impacting electrical properties of the overcoat layer and while improving print quality.
In electrophotographic or electrophotographic printing, the charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as toner. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced or printed. The toner image may then be transferred to a substrate or support member (e.g., paper) directly or through the use of an intermediate transfer member, and the image affixed thereto to form a permanent record of the image to be reproduced or printed. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
The described electrophotographic copying process is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrophotographic printing applications such as, for example, digital laser printing or ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
To charge the surface of a photoreceptor, a contact type charging device has been used. The contact type charging device includes a conductive member which is supplied a voltage from a power source with a D.C. voltage superimposed with a A.C. voltage of no less than twice the level of the D.C. voltage. The charging device contacts the image bearing member (photoreceptor) surface, which is a member to be charged. The outer surface of the image bearing member is charged with the rubbing friction at the contact area. The contact type charging device charges the image bearing member to a predetermined potential. Typically the contact type charger is in the form of a roll charger such as that disclosed in U.S. Pat. No. 4,387,980, the relative portions thereof incorporated herein by reference.
Multilayered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer (sometimes referred to as an “interfacial layer”), a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an optional overcoating layer in either a flexible belt form or a rigid drum configuration. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Multilayered flexible photoreceptor members may include an anti-curl layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
The electrical properties of some photoreceptors can change upon exposure to light, and these undesirable changes can result in poor print quality. Past studies have shown that this problem is caused by light shock, which is in turn due to the interaction of blue light with the photogenerating layer. In the case of organic photoreceptors having an overcoat layer, it has been discovered that the light shock is intrinsic to the overcoat layer itself and strongly wavelength dependent (e.g., the majority of the light shock being caused by 400-500 nm light).
In the case of overcoated drum photoreceptors, light shock occurs during replacement of xerographic customer replacement units (CRU) and/or photoreceptor service where the unit is exposed to ambient light for over 1 to 2 minutes. Standard overcoat layers are known to absorb in the ultraviolet (UV) region of 450 nm or less, indicating that the UV component of sun light or fluorescent room light is the major cause of light shock which is manifested as a local change in image density (darkening or lightening) due to a local change in charge transport properties induced by UV or visual light. The typical life time of the defect can be as long as several days.
Prior solutions focused on the interaction of light with the photogenerating layer but did not address intrinsic overcoat layer light shock protection. For example, U.S. Pat. No. 6,713,220, incorporated herein by reference, discloses a method for reducing the effects of light shock by preventing 400-500 nm light from interacting with the generator layer by doping a light-absorbing material into a charge transport layer comprising arylamine. However, intrinsic light shock observed in organic overcoat layers is not resolved by the method taught by U.S. Pat. No. 6,713,220. Thus, there is a need for a solution to the intrinsic light shock experienced by organic overcoat layers.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrophotographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”